Metal carbide/nitride precipitation control in fusion welding

ABSTRACT

Properties and performance of weld material between metals in a weldment is controlled by modifying one or more of the nitrogen content and the carbon content to produce carbide (e.g. MC-type), nitride and/or complex carbide/nitride (e.g. MX-type) type precipitates. Fusion welding includes (i) adjusting shield gas composition to increase nitrogen/carbon gas and nitride/carbide species, (ii) adjusting composition of nitrogen/carbon in materials that participate in molten welding processes, (iii) direct addition of nitrides/carbides (e.g. powder form), controlled addition of nitride/carbide forming elements (e.g. Ti, Al), or addition of elements that increase/impede solubility of nitrogen/carbon or nitride/carbide promoting elements (e.g. Mn), and (iv) other processes, such as use of fluxes and additive materials. Weld materials have improved resistance to different cracking mechanisms (e.g., hot cracking mechanisms and solid state cracking mechanisms) and improved tensile related mechanical properties.

RELATED APPLICATION DATA

This application is a divisional application of U.S. patent applicationSer. No. 15/437,901 filed Feb. 21, 2017 and is based on and claimspriority to U.S. Application No. 62/298,358, filed Feb. 22, 2016, theentire contents of which are incorporated herein by reference.

This invention was made with support under a sub-contract awarded by acontractor to the federal government. The U.S. government has certainrights in the invention.

FIELD OF THE DISCLOSURE

The present disclosure relates to welding materials and methods ofwelding and the resulting properties of weld materials. Morespecifically, the present disclosure relates to controllingprecipitates, particularly carbide (e.g. MC-type), nitride (e.g.MN-type) and/or complex carbide/nitride (e.g. MX-type) typeprecipitates, in weld material joining bodies, through the control ofone or more of nitrogen content and carbon content in the weldfabrication process, particularly when the weld fabrication process usesERNiCr-3 (filler metal 82) as the weld metal joining dissimilar metalsvia welding. The disclosed welding materials and methods of welding alsoextend to joining of similar metals via welding as well as to otherprocesses and structures associated with overlays, buttering or claddingof non-corrosion resistant base materials with corrosion resistant weldmetals. The present disclosure can also be extended to composition andprecipitate control in base materials, per se.

BACKGROUND

In the discussion that follows, reference is made to certain structuresand/or methods. However, the following references should not beconstrued as an admission that these structures and/or methodsconstitute prior art. Applicants expressly reserve the right todemonstrate that such structures and/or methods do not qualify as priorart against the present invention.

Materials have chemical, microstructural, and mechanical properties thatare a function of composition and processing. While materials will havea composition within specified ranges and/or have a specified processingmethod, the specification does not always state or put limits onspecific interstitial constituents (such as C or N) or specificprocesses that influence every desired property of the material.Furthermore, even when a material is within a specification, there issource-to-source and heat-to-heat variability in the composition of thematerial, which may lead to variability in properties to be outside ofacceptable limits and/or tolerance bands.

This variability applies, for example, to the materials and methods usedin welding. As an example, ERNiCr-3 (a grade of welding wire also knownas Filler Metal 82) is widely used for joining dissimilar metals viafusion welding and is commonly found in, for example, the nuclear powerindustry for dissimilar metal welds in pressurized water reactorcomponents. ERNiCr-3 can be sourced from various manufactures and, whileERNiCr-3 from each manufacturer will be compositional withinspecification, the material specifications and manufacturing methods forthese materials do not control nitrogen content or nitride formationexcept through the control of bulk concentrations of constituentelements and there is variability in material content and materialperformance due to localized variability in composition whereby theERNiCr-3 material still exhibits a wide range of chemical,microstructural, and mechanical properties.

These unspecified compositional variations can impact the performance ofthe weld material joining the two metallic bodies forming a weldment, aswell as the weldment overall. For example, variations in constituentsnot covered by the specification alone or in combination with narrowerranges for constituents covered by the specification for various fusionwelding processes and materials can influence formation of precipitateswithin inter-dendritic and inter-granular sites of the weldmicrostructure and can have an influence on the material properties(among other things, weld crack susceptibility) and result inperformance variability.

SUMMARY

Generally, Applicants have investigated the above-discussed variationsand their effect on composition—structure—property relationships infusion welding and propose solutions applying these relationships toimprovements in fusion welding processes and materials with attendantimprovements in performance of weld materials joining the two metallicbodies forming a weldment, as well as the weldment overall and otherprocesses and structures associated with, for example, overlays,buttering or cladding of non-corrosion resistant base materials withcorrosion resistant weld metals. In particular, Applicants have observedthat variability in material content and performance among weldmaterials, such as those formed using ERNiCr-3 materials, often relatesto the nitrogen content and the carbon content, which influences metalcarbide type (MC-type), nitride (e.g. MN-type), and/or complexcarbide/nitride type (e.g. MX-type) precipitation. It has beendetermined that early formation and presence of high temperaturenitrides have a prominent effect on the volume (via enhanced nucleation)and morphology of carbide or nitride type phases and theproperties/characteristics of accompanying primary/secondary phaseswithin both partially- and fully-solidified materials and in bothferrous and non-ferrous materials. Relatedly, control of nitrogen and/orcarbon content, in particular the amount of high temperature nitrideavailable during joining, such as by welding, and/or carbide formationwithin weld material can provide a method to regulate carbide/nitrideprecipitation and growth and desired material effect(s). Thus,Applicants have developed weld materials and processes for fusionwelding that modifies one or more of the nitrogen content and carboncontent and precipitates in weld materials by one or more of thefollowing: (i) adjusting the shield gas composition to increase nitrogengas and nitride species, (ii) adjusting the shield gas composition todecrease nitrogen gas and nitride species, (iii) adjusting thecomposition of nitrogen, nitride forming and nitride solubilizingconstituents in the materials to obtain a desired concentration ofnitrogen and nitrides, and (iv) using other processes, such as use offluxes and filler materials, to introduce nitrogen or nitrides to themolten metal forming the weld material, overlay, buttering or cladding,(v) adjusting the shield gas composition to increase carbon gas andcarbide species, (vi) adjusting the shield gas composition to decreasecarbon gas and carbide species, (vii) adjusting the composition ofcarbon, carbide forming and carbide solubilizing constituents in thematerials to obtain a desired concentration of carbon and carbides, and(viii) using other processes, such as use of fluxes and fillermaterials, to introduce carbon or carbides to the molten metal formingthe weld material, overlay, buttering or cladding.

In general, exemplary embodiments of a weldment comprises a firstmetallic body and a second metallic body joined by a weld material,wherein the weld material has a composition including 18.0 to 22.0 wt. %Cr, 2.5 to 3.5 wt. % Mn, up to 3.0 wt. % Fe, 15 ppm to 120 ppm or 200ppm to 1500 ppm N, and equal to or greater than 67 wt. % Ni.Alternatively, the weld material has a composition including 18.0 to22.0 wt. % Cr, 2.5 to 3.5 wt. % Mn, up to 3.0 wt. % Fe, 100 ppm to 500ppm N, 0.03 to 0.06 wt. % C, and equal to or greater than 67 wt. % Ni.Further alternatively, the weld material has a composition including18.0 to 22.0 wt. % Cr, 2.5 to 3.5 wt. % Mn, up to 3.0 wt. % Fe, up to250 ppm N, up to 0.040 wt. % C, and equal to or greater than 67 wt. %.In each of the above embodiments, other elements may be present asfollows: Nb+Ta 2.0 to 3.0 wt. %, max 0.75 wt. % Ti, and other elements(total) max 0.50 wt. %. In the case of overlays and cladding, exemplaryembodiments may utilize one metallic body, and may utilize a secondmetallic body that is a base material component or a weld deposit. Infurther embodiments, the weldment can include multiple base materialcomponents and one or multiple weld material components.

An exemplary method of fusion welding comprises forming a region ofmolten material between a first metallic body and a second metallicbody, wherein the molten material includes molten base metal from thefirst metallic body, molten base metal from the second metallic body,weld metal from a welding alloy, and, optionally, one or more moltenadditive material, modifying at least one of a nitrogen content of themolten material and a nitride content of the molten material, coalescingthe molten material, and solidifying the molten material to form a weldmaterial, wherein the solidified weld material joins the first metallicbody to the second metallic body to form a weldment, and wherein thesolidified weld material has a composition including 15 ppm to 120 ppmor 200 ppm to 1500 ppm nitrogen. In an alternative embodiment, at leastone of a nitrogen or carbon content of the molten material and a nitrideor carbide content of the molten material is modified and the solidifiedweld material has a composition including one or more of 100 ppm to 500ppm N and up to 0.06 wt. % C (preferably, 0.03 to 0.06 wt. % C). In afurther alternative embodiment, the solidified weld material has acomposition including one or more of up to 250 ppm N and up to 0.040 wt.% C.

Also, in exemplary embodiments, a microstructure of the weld materialincludes a plurality of precipitates, wherein the plurality ofprecipitates include one or more of a plurality of metal carbideprecipitates and a plurality of metal carbide/nitride precipitates. Inexemplary embodiments, a volume fraction of the plurality ofprecipitates is 0.0025 or less for nitrogen in the range of 15 ppm to120 ppm (alternately, 0.0018 or less for nitrogen in the range of 15 ppmto 100 ppm) and is 0.003 or more for nitrogen in the range of 200 ppm to1500 ppm (alternately at or above 0.010, alternatively from 0.010 to0.0175, for nitrogen in the range of greater than 1000 ppm,alternatively from 1000 ppm to 1300 ppm) The above precipitate volumefractions were observed for ERNiCr-3/EN82 wire with a fixed carboncontent of nominally 0.05 wt. % (for example ranging from 0.050 to 0.055as reported in Table 2). In other exemplary embodiments, the volumefraction of the plurality of precipitates is 0.0025 to 0.0077 fornitrogen in the range of 100 ppm to 500 ppm and 0.03 to 0.05 wt. % C,alternately, 0.0025 to 0.0060 for nitrogen in the range of 125 ppm to350 ppm in combination with 0.030 wt. % C and 0.0060 to 0.0077 fornitrogen in the range of 200 ppm to 310 ppm in combination with 0.05 wt.% C. In this embodiment, precipitate volume fractions were observed fortwo different samples of ERNiCr-3/EN82 wire each with a fixed carboncontent of, in one case nominally 0.05 wt. % (for example ranging from0.051 to 0.055 as reported in Table 5) and in a second case nominally0.03 wt. % (for example ranging from 0.027 to 0.030 as reported in Table5).

All values used in the discussion of embodiments herein are reported asnominal (whether or not that term is used in the text) and all values inexamples and tests are reported as actual.

BRIEF DESCRIPTION OF THE DRAWING

The following detailed description of preferred embodiments can be readin connection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIG. 1A is a schematic cross-sectional side view of an exemplaryembodiment of a weldment showing the weld material and certain zoneswithin the weldment.

FIG. 1B a schematic cross-sectional side view of an exemplary embodimentof a weld overlay.

FIG. 1C a schematic cross-sectional side view of an exemplary embodimentof weld buttering.

FIG. 2 is a scanning electron microscope image of an ERNiCr-3 weldmaterial prepared using a shield gas of 95 mol. % argon and 5 mol. %nitrogen.

FIGS. 3A-H are a series of SEM micrographs of ERNiCr-3 weld materialprepared using a shield gas with varying amounts of nitrogen content.

DETAILED DESCRIPTION

Fusion welding joins a first metallic body to a second metallic body toform a weldment. Because metals must be heated to the melting point forfusion welds to be produced, the first metallic body and the secondmetallic body are sufficiently heated to form molten base material fromeach and, with any added material such as weld wire and filler material,to form a region of molten material. The region of molten materialcoalesces by which the different molten constituents mix together toform a molten mass. There is often a high degree of homogeneity amongthe component metals that have been melted, but localized compositionalvariation can occur. The coalescence typically occurs by convection, butoscillation and even evaporation can also play a role. The coalescedmolten region then solidifies to form weld material that joins the firstmetallic body to the second metallic body to form the weldment.

FIG. 1A shows a simplified schematic cross-section of a portion of aweldment 10 at the fusion weld joint. The weldment comprises a firstmetallic body 20 and a second metallic body 30 joined by a weld material40. The weld material 40 is a mixture of base materials from the firstmetallic body 20 and the second metallic body 30 that have completelymelted and any added material such as weld wire and filler material. Ata distance from and outside the weld material 40 and separated therefromby an interface/partially melted zone 50, there is a heat affected zone(HAZ) 60. The heat affected zone is a volume of material in the firstmetallic body 20 and in the second metallic body 30 in which the basemetal, while not melted, still has had its microstructural or mechanicalproperties altered by high temperature heat from the welding process. Ata further distance from the weld material 40 and outside the heataffected zone 60, the base metal of the first metallic body 20 and thesecond metallic body 30 is essentially unaffected. In the illustratedportion of weldment 10, the regions in the metallic bodies 20, 30 wherethe base metal is essentially unaffected are indicated by 70 and 80,respectively.

The disclosed fusion welding also extends to other applications, such asa weld overlay, buttering, and cladding. FIG. 1B shows a simplifiedschematic cross-section of a portion of a weld overlay. The weld overlay200 applies one or more metals with specific characteristics to a basemetal or base structure to improve desirable properties or to restorethe original dimension of the component. As shown in FIG. 1B, the weldoverlay 200 comprises a weld overlay material 202 to a base structure204 (in FIG. 1B, the base structure is a pipe). A weld material 206 islocated at a joint or contact point between two sections of the basematerial 204 and the weld material 202 extends along a surface of thebase structure 204 past a defect 208 (in FIG. 1B, the defect is acrack). FIG. 1C shows a simplified schematic cross-section of a portionof weld buttering 240, in which a layer of weld metal 242 has beensequentially applied over a base metal 244 to form multiple layers ofweld metal. Although FIG. 1 C illustrates weld deposits applied parallelto the weldment surface, weld deposits may also be applied perpendicularto the weldment surface.

In exemplary embodiments, the weld material 40, 206, 242 (and optionallythe weld overlay material 202) is based on ERNiCr-3 weld metal. ERNiCr-3weld metal provides excellent corrosion resistance and high temperaturemechanical properties while providing a means to bridge the differencesin coefficient of thermal expansion between the first metallic body andthe second metallic body when using dissimilar metals, such as ferriticand austenitic materials. Although ERNiCr-3 weld metal is generallyconsidered to be resistant to mechanical flaws and defects such assolidification cracking, solidification cracking has been observed inhigh restraint situations. Examples of high restraint situations includethick section weld deposits, highly restrained metallic bodies, andmetallic bodies with high yield strength. Furthermore, it has beenobserved that considerable heat-to-heat variability in susceptibility tosolidification cracking occurs despite only slight variations inchemical composition within the specification range of conventionalERNiCr-3 weld metal. One test by which such solidification cracking canbe observed and compared between samples is the cast pin tear test(CPTT), which is disclosed and described in T. Alexandrov, et al., “Useof the cast pin tear test to study solidification cracking”, Weld World(2013) 57:635-648, the entire contents of which is incorporated hereinby reference.

One or more of the nitrogen content and the carbon content and theprecipitate properties (number, size and/or distribution) of the weldmaterial influence the material strength of the weld material as well ascertain types of crack resistance of the weld material. Applicants havedetermined that control of nitrogen and nitride content in the weldmaterial can be achieved by control of nitrogen sources and nitridesources to the weld environment and can be used to achieve desiredproperties in the weld material, including a reduction in certaincracking susceptibility and improved mechanical strength. Similarly,control of carbon and carbon content in the weld material can beachieved by control of carbon sources and carbide sources to the weldenvironment and can be used to achieve desired properties in the weldmaterial, including a reduction in certain cracking susceptibility andimproved mechanical strength. Additionally, combining both nitrogen andcarbon control can be used to achieve such desirable properties.

For example, in a first embodiment, a range of 15 ppm to 120 ppmnitrogen appears to provide resistance to hot cracking mechanisms, suchas solidification cracking, while heats with nitrogen content of 150 ppmto 250 ppm appear to be more susceptible. Conversely, higher nitrogencontents in the range of 200 ppm to 1500 ppm appear to improvemechanical strength and promote resistance to solid state crackmechanisms such as ductility dip cracking (DDC).

Nitrogen content in the range of 15 ppm to 120 ppm, alternatively 20 ppmto 100 ppm and a low volume fraction of precipitates (e.g., less than0.005) have little impact on mechanical properties such as tensilestrength and 0.2% yield strength, and improves resistance of the weldmaterial to hot cracking mechanisms, such as solidification cracking.Also, nitrogen content in the range of 200 ppm to 1500 ppm,alternatively 600 ppm to 1300 ppm and a high volume fraction ofprecipitates (e.g., more than 0.01, alternatively, 0.01 to 0.0175)increases mechanical properties of the weld material such as tensilestrength and 0.2% yield strength, and improves resistance of the weldmaterial to solid state cracking mechanisms, such as ductility dipcracking.

Considering the above, a specific embodiment of a weld material has acomposition that includes nitrogen content in a range of 15 ppm to 120ppm or in the range of 200 ppm to 1500 ppm. In addition, amicrostructure of the weld material includes one or more of a pluralityof metal carbide precipitates and a plurality of metal carbide/nitrideprecipitates. When the nitrogen content is in the range of 15 ppm to 120ppm, the microstructure of the weld material includes a plurality ofprecipitates having a volume fraction of 0.0025 or less; when thenitrogen content is in the range of 200 ppm to 1500 ppm, themicrostructure of the weld material includes a plurality of precipitateshaving a volume fraction of 0.003 or more. The volume fraction ofprecipitates can be determined by quantitative image analysis with SEM(as discussed further below).

Also for example, in a second embodiment, one or more of 100 ppm to 500ppm N and up to 0.06 wt. % C (preferably, 0.03 to 0.06 wt. % C) providesimprovement in mechanical performance. More particularly, a range of upto 250 ppm N in combination with a range of up to 0.040 wt. % C providesresistance to hot cracking mechanisms, such as solidification cracking.Conversely, a range of 100 ppm to 500 ppm N in combination with a rangeof 0.03 wt. % C to 0.06 wt. % C improves mechanical strength andpromotes resistance to solid state crack mechanisms such as ductilitydip cracking (DDC).

The following Table 1 summarizes compositions of ERNiCr-3 weld materialwhere the carbon content and the nitrogen content are controlled toobtain the specified compositions and with attendant effects on hotcracking mechanisms, such as solidification cracking and solid statecrack mechanisms such as ductility dip cracking (DDC).

TABLE 1 Composition for improved Composition for improved solidificationcrack ductility dip cracking resistance resistance (DDC) Constituent MinMax Min Max C — 0.040 0.03 0.06 Cr 18   22 18 22 Fe — 3.00 — 3.00 Mn 2.50 3.50 2.50 3.50 N — 0.0250 0.0100 0.0500 Nb + Ta  2.0 3.0 2.0 3.0Ni 67.0 — 67.0 — Ti — 0.75 — 0.75 Other — 0.500 — 0.500 Elements (Total)

Considering the above, a specific embodiment of a weld material has acomposition that includes nitrogen content in a range of up to 250 ppmnitrogen in combination with carbon content in a range of up to 0.040wt. % C. In addition, a microstructure of this weld material includesone or more of a plurality of metal carbide precipitates and a pluralityof metal carbide/nitride precipitates. In particular, the microstructureof this weld material includes a plurality of precipitates having avolume fraction of about 0.0025. Another specific embodiment of a weldmaterial has a composition that includes nitrogen content in a range of100 ppm to 500 ppm nitrogen in combination with carbon content in arange of 0.03 wt. % C to 0.06 wt. % C. In addition, a microstructure ofthis weld material includes one or more of a plurality of metal carbideprecipitates and a plurality of metal carbide/nitride precipitates. Inparticular, the microstructure of this weld material includes aplurality of precipitates having a volume fraction of plurality ofprecipitates of 0.0025 to 0.0077 for nitrogen in the range of 100 ppm to500 ppm and 0.03 to 0.05 wt. % C, alternately, 0.0025 to 0.0060 fornitrogen in the range of 125 ppm to 350 ppm in combination with 0.030wt. % C and 0.0060 to 0.0077 for nitrogen in the range of 200 ppm to 310ppm in combination with 0.05 wt. % C. The volume fraction ofprecipitates can be determined by quantitative image analysis with SEM(as discussed further below) and provides a metric to correlate with theknown resistance to hot cracking mechanisms, such as solidificationcracking, in high restraint applications.

FIG. 2 is a scanning electron microscope image of an ERNiCr-3 weldmaterial prepared using a shield gas of 95 mol. % argon and 5 mol. %nitrogen. The ERNiCr-3 weld material in FIG. 2 had a nitrogen content of1300 PPM. In the FIG. 2 image 100, the light or white areas 110 arecarbide (e.g. MC-type) and complex carbide/nitride (e.g. MX-type) typeprecipitates. The black lines 120 in the micrograph are grainboundaries. The image 100 was taken at 20.0 kv and 1500× magnification.Using quantitative image analysis and taking the average of measurementsfrom fifteen SEM micrographs (all from the same orthogonal plane of thesample and using the same weld process and consistent imaging andquantification settings), the volume fraction of precipitates for thesample shown in the image 100 in FIG. 2 was determined to be 0.0175.Other features visible in FIG. 2 include gamma phase (i.e. austenite)130, small MC/MX phase particles (inter-granular) 140, small MC/MX phaseparticles (inter-dendritic) 150, and large MN/MX phase particles 160.

The amount of precipitates in the weld material can be influenced by thepresence and amount of nitride and carbide forming constituents.Dominate carbide or nitride forming constituents for ERNiCR-3 areniobium and titanium. Niobium is the primary carbide forming element inERNiCr-3. The traditional phase transformation sequence for ERNiCr-3only results in gamma phase (i.e., austenite) and NbC. Therefore, in aspecific example, the composition of the weld material can include oneor more of 1-4 wt. % Nb, alternatively 2-3 wt. % Nb, and up to 0.75 wt.% Ti, alternatively, 0.30 to 0.45 wt. % Ti.

In other respects, the weld material can be any weld material suitablefor joining the first metallic body and the second metallic body to forma weldment. In a further specific embodiment, the first metallic bodyand the second metallic body are formed of similar metals or dissimilarmetals (alternatively are ferrous and non-ferrous metals), and the weldmaterial is an ERNiCr-3 based weld material.

In a first embodiment, the ERNiCr-3 based weld material has acomposition that includes:

Cr 18.0 to 22.0 wt. %, Mn 2.5 to 3.5 wt. %, Fe 1.0 to 3.0 wt. %, M up to4.0 wt. % N 15 ppm to 120 ppm or 200 ppm to 1500 ppm, Si up to 0.25 wt.%, and Ni equal to or greater than 67 wt. %,

In a second embodiment, the ERNiCr-3 based weld material has acomposition that includes:

Cr 18.0 to 22.0 wt. %, Mn 2.5 to 3.5 wt. %, Fe up to 3.0 wt. %, M up to4.0 wt. % N 100 ppm to 500 ppm, C 0.03 to 0.06 wt. %, Si up to 0.25 wt.%, and Ni equal to or greater than 67 wt. %,

In a third embodiment, the ERNiCr-3 based weld material has acomposition that includes:

Cr 18.0 to 22.0 wt. %, Mn 2.5 to 3.5 wt. %, Fe up to 3.0 wt. %, M up to4.0 wt. % N up to 250 ppm, C up to 0.040 wt. %, Si up to 0.25 wt. %, andNi equal to or greater than 67 wt. %

In each of the above, M is a carbide or nitride or complexcarbide/nitride forming constituent such as Nb or Ti. When Nb ispresent, its limit is 1-4 wt. %, alternatively, 2-3 wt. %; when Ti ispresent, its limit is up to 0.75 wt. %, alternatively, 0.30 to 0.45 wt.%. Nb and Ta are primary carbide forming elements in ERNiCr-3 and can besubstituted for each other; when present, the traditional phasetransformation sequence for ERNiCr-3 results in gamma phase and NbCand/or TaC.

Carbon can also be present in the weld composition and can contribute tothe precipitate properties (number, size and/or distribution) of theweld material and has a prominent influence on precipitation volume. Inthe specification for ERNiCr-3 (EN82H) material, C has a range of 0.03wt. % to 0.10 wt. %. Typical bulk composition is 0.035-0.045 wt. % C,and observations on heats with elevated carbon content (0.050-0.060 wt.% C) suggest that, while nitrides are still the primary catalyst forheterogeneous precipitation, N and C both contribute to the precipitatevolume in the weld material.

Within a single weldment, specific regions can employ more or lessnitrogen and/or precipitates to obtain desired properties. For example,in a weldment with a multi-layer weld deposit, different regions orlayers of the weldment can have weld material with different amounts ofnitrogen in the weld material composition. In regions of the weldmentwith a higher susceptibility to solidification cracking (which typicallyoccurs towards the end of weld solidification), the nitrogen content ofthe weld material can be adjusted to be 15 ppm to 120 ppm (approximately0.0015 wt. % to 0.012 wt. %) to provide increased resistance tosolidification cracking or can be adjusted to have both nitrogen andcarbon where nitrogen is present up to 250 ppm (approximately 0.025 wt.%) in combination with carbon present up to 400 ppm (approximately 0.040wt. %). Within the same weldment but at a different layer, some regionshave a lower susceptibility to solidification cracking but a highersusceptibility to solid state crack mechanisms such as ductility dipcracking (for example, regions containing migrated weld grain boundariesor insufficient MC-type carbide precipitates) and the weld material inthese regions can have a composition in which the nitrogen level isadjusted to be 200 ppm to 1500 ppm, alternatively 500 ppm to 1400 ppm or1000 ppm to 1300 ppm (approximately 0.02 wt. % to 0.15 wt. %,alternatively 0.05 wt. % to 0.14 wt. % or 0.10 wt. % to 0.13 wt. %) orcan be adjusted to have both nitrogen and carbon where nitrogen ispresent in a range of 100 ppm to 500 ppm (approximately 0.010 wt. % to0.050 wt. %) in combination with carbon present in a range of 300 ppm to600 ppm (approximately 0.03 wt. % to 0.06 wt. %). It is alsocontemplated that in some instances, the nitrogen and/or carbon contentof weld material within the same weldment but at a different layer canbe unadjusted.

Without being bound to any particular theory, it is currently understoodthat solidification of weld material in the welding process occurssufficiently rapidly that metal element-based (such as Nb-based) orcarbon-based routes to forming carbide (e.g. MC-type), nitride and/orcomplex carbide/nitride (e.g. MX-type) type particulates in the weldmaterial have only limited time to nucleate, grow and form precipitatesbefore such precipitate forming processes are essentially stopped by thesolidification of the weld material. Under these conditions, there islittle to no ability to influence variations in the final precipitateproperties (number, size and/or distribution) in the weld material.However, increasing the presence of nitrogen (or nitrides) in the moltenweld material increases the liquidus temperature, allowing for moremobility of constituents of the weld material composition and a longersolidification process, both of which promote increased precipitateproperties (number, size and/or distribution) as compared to weldmaterial with lower amounts of nitrogen, e.g. less than about 120 ppmnitrogen. These increased precipitate properties (number, size and/ordistribution) have been correlated qualitatively such that an increasein nitrogen/nitride concentrations will increase precipitate propertiesand a decrease in nitrogen/nitride concentrations will decreaseprecipitate properties.

Additionally, weld materials having low nitrogen content (15 ppm to 120ppm) and low volume fraction of precipitates (less than 0.0025) havelittle to no improvement in mechanical properties as compared to weldmaterial in which the nitrogen and precipitates have not be modified,but do display improved resistance to hot cracking mechanisms.Similarly, weld materials having high nitrogen content (200 ppm to 1500ppm and particularly if greater than 1000 ppm) and high volume fractionof precipitates (above 0.003 and particular at or above 0.010,alternatively from 0.010 to 0.0175) have improvements in mechanicalproperties as compared to weld material in which the nitrogen andprecipitates have not been modified, and also display improvedresistance to solid state cracking mechanisms.

Turning to a method of fusion welding in which a weld material joins afirst metallic body to a second metallic body to form a weldment, anexemplary method includes forming a region of molten material between afirst metallic body and the second metallic body. This molten materialincludes molten base metal from the first metallic body, molten basemetal from the second metallic body, weld metal from a welding alloy,and, optionally, one or more molten filler metals. At least one of thenitrogen and the carbon content of the molten material is modified, asdiscussed further below, and the molten material, coalesces, by whichthe different constituents of the molten base metal from the firstmetallic body, molten base metal from the second metallic body, weldmetal from a welding alloy, and, optionally, one or more molten fillermetals join together and become a mixture. The coalesced molten materialthen solidifies to form a weld material that has a composition,depending on the disclosed embodiment used, that includes 15 ppm to 120ppm or 200 ppm to 1500 ppm nitrogen, or includes both nitrogen andcarbon where nitrogen is present up to 250 ppm in combination withcarbon present up to 0.040 wt. %, or includes both nitrogen and carbonwhere nitrogen is present in a range of 100 ppm to 500 ppm incombination with carbon present in a range of 0.03 wt. % to 0.06 wt. %(depending on the desired mechanical properties and desired crackresistance).

In addition, modifying the nitrogen and nitride content of the moltenmaterial modifies the microstructure of the weld material to include oneor more of a plurality of metal carbide precipitates and a plurality ofmetal carbide/nitride precipitates. In exemplary embodiments, themicrostructure of the weld material includes a plurality of NbCprecipitates and/or TiN precipitates at a low volume fraction ofprecipitates (less than 0.0025) to improve resistance to hot crackingmechanisms or at a high volume fraction of precipitates (above 0.003 andparticular at or above 0.010) to improve resistance to solid statecracking mechanisms. In alternative embodiments in which carbon andnitrogen are controlled, a volume fraction of precipitates is 0.0025 to0.0077 for nitrogen in the range of 100 ppm to 500 ppm in combinationwith 0.03 to 0.05 wt. % C, alternately, the volume fraction is 0.0025 to0.0060 for nitrogen in the range of 125 ppm to 350 ppm in combinationwith 0.030 wt. % C and 0.0060 to 0.0077 for nitrogen in the range of 200ppm to 310 ppm in combination with 0.05 wt. % C.

Methods disclosed herein modify the nitrogen content and or the carboncontent of the molten material by controlling the presence of nitrogen(and nitrides) and/or carbon (and carbides) in the molten weld material.Controlling the presence of nitrogen (and nitrides) and/or carbon (andcarbides) in the molten weld material also influences and modifies thepresence of nitrogen and carbide (e.g. MC-type) type precipitates and/orcomplex carbide/nitride (e.g. MX-type) type precipitates and theircontent in the weld material. For example, a welding process can be usedwhich includes one or more of the following steps to modify one or moreof the nitrogen content and the carbon content of the molten material:(i) the shield gas composition is adjusted to increase nitrogen gas andnitride species, (ii) the shield gas composition is adjusted to decreasenitrogen gas and nitride species, (iii) the composition of nitrogen andnitride forming and nitride solubilizing constituents in the materialsis adjusted to obtain a desired concentration of nitrogen and nitrides,and (iv) the use of other processes, such as the use of fluxes andfiller materials, are used to introduce nitrogen or nitrides to themolten metal forming the weld material, (v) adjusting the shield gascomposition to increase carbon gas and carbide species, (vi) adjustingthe shield gas composition to decrease carbon gas and carbide species,(vii) adjusting the composition of carbon, carbide forming and carbidesolubilizing constituents in the materials to obtain a desiredconcentration of carbon and carbides, and (viii) using other processes,such as use of fluxes and filler materials, to introduce carbon orcarbides to the molten metal forming the weld material, overlay,buttering or cladding.

After preparing the workpieces (e.g., the metallic bodies that will bejoined by the weld material to form the weldment) and materials forwelding, for example by shaping and/or cleaning, the welding process cancommence and proceed to the point at which a region of molten materialis formed between the first metallic body and the second metallic body.This region of molten material includes molten base metal from the firstmetallic body, molten base metal from the second metallic body, moltenweld metal from a welding alloy, and, optionally, one or more moltenfiller metals.

If a shield gas is present, such as in gas metal arc welding and gastungsten arc welding, the shield gas is supplied to the region of themolten material and forms a protective gaseous barrier to oxygen, watervapor and other impurities that can reduce the quality of the weld. Theshield gas can be supplied by any suitable means. For example, theshield gas can be supplied through a shield gas line leading to a gasnozzle at the end of the welding line where the shield gas is expelledto the welding work zone around the welding arc or the shield gas can besupplied from a separate source and device and be applied to the weldingwork zone around the welding arc.

As an example of a shield gas, the shield gas can be an inert orsemi-inert gas (such as argon or helium) whose composition has beenmodified to include one or more of from 0 to 5 mol. % nitrogen and from0 to 25 mol. % CO₂ (whether individual gases or a mixed gas). As anexample, a nitrogen only shield gas, when used in welding applications(such as automatic gas tungsten arc welding with cold wire (AGTA-CW))with an ERNiCr-3 welding consumable, forms a weld material that includesMC-type and MX-type precipitates at a volume fraction of up to 0.0175and that has a composition that includes up to 0.13 wt. % nitrogen.

In the welding work zone around the welding arc, the protective gaseousbarrier of the shield gas is in contact with the molten material andnitrogen (either in the form of elemental nitrogen or, due to the hightemperatures used in welding, a nitride) or carbon (either in the formof elemental carbon or, due to the high temperatures used in welding, acarbide) from the gaseous barrier is introduced into the moltenmaterial. In the molten material and during solidification, the nitrogen(or nitride) and/or carbon (or carbide) remains as nitrogen/carbon orreacts with nitride/carbide forming species in the molten metal to formnitrides/carbides, which themselves then promote carbide (e.g. MC-type)and/or complex carbide/nitride (e.g. MX-type) type particulate as wellas contribute to the nitrogen content of the weld material.

Alternatively or concurrently, the amount of nitrogen (or nitride) orcarbon (or carbide) material in the weld material can be controlled bythe composition of nitrogen (and/or carbon) forming and nitrogen (and/orcarbon) solubilizing constituents in the materials of one or more of thefirst metallic body and the second metallic body and the weld metal ofthe welding alloy. The amount of nitrogen and nitrides (and/or carbonand carbides) can be influenced by adding nitrogen/nitride (and/orcarbon/carbide) forming elements or adding elements that increase orimpede solubility of nitrogen or nitride promoting elements (and/orcarbon or carbide promoting elements). As examples, Ti and Al can beused as nitrogen/nitride forming elements, and Mn can be used as anelement to promote the formation of nitrogen or nitrides. These twotypes of additions can be used singly or in combination to balance thedesired effect on the amount and distribution of nitrogen and thecarbide (e.g. MC-type), nitride and/or complex carbide/nitride (e.g.MX-type) type particulate, as well as contribute to the nitrogen contentof the weld material. For example, one or both of the first metallicbody and the second metallic body can have a composition in which thenitrogen content and/or the nitride content has been modified. Asanother example, one can use measured additions of nitrogen/nitridesduring primary/secondary melt processing, such as during VIM melting ora pressurized electroslag remelting process (P-ESR). The analogoussituation can be arrived at for carbon content and/or carbide content byusing carbon/carbide forming elements and/or processes. For example,carbon/carbide forming elements can be incorporated into weldingsupplies, such as weld wire, during the VIM melting of the material.

As a further example, the nitrogen content in weld metal of the weldingconsumable, for example ERNiCr-3 weld metal, can be modified to includenitrogen and/or nitrides by, for example, nitriding the weld metal or bycoating the weld metal. Carbon content can be similarly adjusted by, forexample, carbiding the weld metal or by coating the weld metal. Tonitride or carbide the weld metal, one can expose conventional weldmetal to a nitrogen/carbon containing atmosphere at temperature and/orpressure to nitride/carbide the weld metal and form a nitrogenenriched/carbon enriched surface zone in the weld metal. Thisnitrided/carbided weld metal can then be used as a welding consumable ina welding process by which the nitride/carbide material of the weldmetal is added to the region of molten material. Varying the amount ofnitriding/carbiding of the weld metal thereby modifies the amount ofnitrogen/carbon in the composition of the molten material. Certainflux-based or powder core products could also be modified/created tosimilar effect.

Alternatively or concurrently, the amount of nitrogen (or nitride)material in the weld material can be controlled by the composition ofnitrogen, nitride forming and nitride solubilizing constituents in thematerials of the welding aides used in the welding process. Similarly,the amount of carbon (or carbide) material in the weld material can becontrolled by the composition of carbon, carbide forming and carbidesolubilizing constituents in the materials of the welding aides used inthe welding process. Examples of welding aides include fluxes andfillers. For example, in shielded metal arc welding (SMAW) with anERNiCrFe-3 welding consumable, when the flux is heated and flows itcontacts the region of molten material and forms a protective barrier tooxygen, water vapor and other impurities that can reduce the quality ofthe weld. Although the flux does not mix with the molten material, atthe interface of flux and molten material the constituents from the fluxcan enter into the molten composition. This can occur when there issufficient driving force for such constituents to cross the flux-moltenmaterial interface, such as the high temperatures used in welding or thechemical potentials of the molten material and the flux. If one or moreadditive is used, such as nitride powders, carbon powders, nitrideforming elements, carbide forming elements, and coatings that generatenitrogen gas and/or carbon gas during welding, the additives melt andtheir content contributes to the content of the molten material.Modifying the nitrogen, nitrides, nitride forming and nitridesolubilizing, carbon, carbides, carbon forming and carbide solubilizingcontent of the fillers, by for example modifying the composition,nitriding, carbiding, or coating, varies the amount of nitrogen, carbon,nitrides, carbides, nitride forming and nitride solubilizing and carbideforming and carbide solubilizing content in the material and, when thematerial is used as a consumable in a welding process, modifies theamount of nitrogen and/or carbon in the composition of the moltenmaterial.

EXAMPLES

Tables 2 and 3 report results from compositional analysis and mechanicaltesting on samples with varying amounts of nitrogen in the weldmaterial. The samples were prepared by manufacturing a weldment usingAGTA-CW welding and a metallic body of Alloy 600 (UNS06600), anickel-chromium-iron alloy. The weld beads were deposited in flatposition on the Alloy 600 test coupon; producing a multi-layer weldbuildup with an approximate geometry of 4 inch (width)×5 inch (length)×1inch (height). The weld metal of the samples in Tables 2 and 3 was anERNiCr-3 based weld metal. No additive or flux was used. During thewelding process for the samples in Table 2 and 3, argon-mixed shield gaswas used that had a nitrogen content that varied between the foursamples as follows: a 0 mole percent (mol. %) nitrogen shield gas wasused for sample YT0159-0NC, a 1 mol. % nitrogen shield gas was used forsample YT0159-1NC, a 5 mol. % nitrogen shield gas was used for sampleYT0159-5NC, and a 20 mol. % nitrogen shield gas was used for sampleYT0159-20NC).

The ERNiCr-3 weld metal of the samples in Tables 2 and 3 had beenprepared by vacuum melting technique in a three-step melt processincluding vacuum induction melting (VIM), electroslag remelting (ESR),and vacuum arc remelting (VAR), which results in nitrogen content in therange of 15 ppm to 25 ppm. ERNiCr-3 that has been prepared by vacuummelting techniques is a preferred weld consumable as compared to airmelt ERNiCr-3 because the nitrogen and nitride content in vacuum meltERNiCr-3 is more consistent between samples and also the nitrogen andnitride content is 15 ppm to 25 ppm, which is sufficiently low thatcontrol of the nitrogen and nitride content in the weld material can beessentially completely dependent on and controlled by the amount ofnitrogen and nitrides added by the user during the welding process,e.g., through control of one or more of the shield gas composition, thecomposition of nitrogen (and nitride) forming and nitrogen (and nitride)solubilizing constituents in the materials, and other processes such asuse of fluxes and additive materials.

TABLE 2 Compositional Analysis of Weld Materials (in weight %) Ele-Sample Sample Sample Sample ment YT0159-0NC YT0159-1NC YT0159-5NCYT0159-20NC Al 0.053 0.059 0.053 0.064 C 0.053 0.053 0.055 0.051 Co0.007 0.008 0.005 0.009 Cr 20.21  20.18  20.23  20.20  Cu 0.003 0.0030.003 0.003 Fe 1.13  1.11  1.13  1.13  Ga 0.001 0.001 0.001 0.001 H   0.00043 *    0.00086 *    0.00046 *   0.0002 * La <0.001  <0.001 <0.001  <0.001  Mg <0.001  <0.001  <0.001  <0.001  Mn 3.29  3.30  3.29 3.31  Mo 0.004 0.004 0.004 0.004 N    0.00186 *  0.060 *  0.136* 0.14*Na <0.005  <0.005  <0.005  <0.005  Nb 2.34  2.31  2.33  2.34  Ni 72.4  72.4   72.3   72.3   O  <0.001 *  <0.001 *  <0.001 *  <0.001 * P <0.005 <0.005  <0.005  <0.005  Pb <0.001  <0.001  <0.001  <0.001  S <0.001 <0.001  <0.001  <0.001  Sb <0.001  <0.001  <0.001  <0.001  Si 0.11 0.11  0.11  0.12  Ta — 0.002 0.002 0.002 Th <0.001  <0.001  <0.001 <0.001  Ti 0.37  0.36  0.36  0.32  V 0.004 0.004 0.004 0.004 W 0.0150.015 0.004 0.032 * = average of three measurements

The results for the compositional analysis reported in Table 2 wereobtained using standard analytical techniques, such as inductivelycoupled plasma mass spectrometry (ICP-MS) and combustion techniques ineither induction or resistance furnaces. The combustion techniques wereused for carbon, hydrogen, nitrogen, oxygen and sulfur. The reportednickel content is based on the balance of the as-measured contents ofthe other constituents.

Sample YT0159-0NC (prepared using a shield gas with 0 nol. % nitrogen),Sample YT0159-1NC (prepared using a shield gas with 1 mol. % nitrogen),Sample YT0159-5NC (prepared using a shield gas with 5 mol. % nitrogen)and Sample YT0159-20NC (prepared using a shield gas with 20 mol. %nitrogen) were then tested for mechanical properties. Table 3 containsthe testing results and, for each sample, reports tensile strength (inksi), 0.2% yield strength (in ksi), elongation (in % in 4D) (meaning the% elongation was measured in a specimen whose gage length is 4 times itsgage diameter) and reduction of area (in %) in both the longitudinaldirection and the transverse direction relative to the weld traveldirection.

TABLE 3 Tensile Testing of Weld Materials Reduction Direction ofDiameter Tensile Yield, 0.2% Elongation of Area Sample measurement (in.)(ksi) (ksi) (% in 4D) (%) YT0159-0NC longitudinal 0.247 97.0 62.5 42 46transverse 0.246 94.0 63.0 36 43 YT0159-1NC longitudinal 0.247 99.0 64.537 51 transverse 0.246 97.5 61.5 38 42 YT0159-5NC longitudinal 0.246 10469.0 35 38 transverse 0.246 107 73.5 28 38 YT0159- longitudinal 0.246102 67.5 31 39 20NC transverse 0.246 107 72.5 35 40

More specifically, the four samples were tested following AWS B4.0(Standard Methods for Mechanical Testing of Welds) with reference toASTM E8-15a (Standard Test Methods for Tension Testing of MetallicMaterials). The testing was conducted at room temperature at 0.005in/in/min strain rate until 1.5% total strain and at 0.050 in/in/mincrosshead rate thereafter until failure. Each sample consisted of allweld metal (corresponding to the compositions in Table 2) and the testblanks for each sample were ⅝ in ×⅝ in ×3.5 in, machined to 0.250 indiameter round tensile specimens.

Comparing the mechanical properties of the samples prepared using ashield gas with >0 mol. % nitrogen to the sample prepared using a shieldgas with 0 mol. % nitrogen, one can observe the change in mechanicalproperties as the amount of nitrogen in the shield gas (and, by proxythe amount of nitrogen in the weld material, increase. The changes intensile strength (absolute and in percentage) are shown in Table 4.

TABLE 4 Comparison of mechanical properties of samples prepared with 1mol. %, 5 mol. % and 20 mol. % nitrogen shield gas to mechanicalproperties of a sample prepared with 0 mol. % nitrogen shield gas Changein Change in Yield Direction of Tensile Strength Strength, 0.2% Samplemeasurement (ksi/%) (ksi/%) YT0159-1NC longitudinal 2.0 ksi/2.1% 2.0ksi/3.2% transverse 3.5 ksi/3.7% −1.5 ksi/−2.4% YT0159-5NC longitudinal7.0 ksi/7.2%  6.5 ksi/10.4% transverse 13.0 ksi/13.8% 10.5 ksi/16.7%YT0159-20NC longitudinal 5.0 ksi/5.2% 5.0 ksi/8.0% transverse 13.0ksi/13.8%  9.5 ksi/15.1%

Also for comparison, per Annex A of ASME IIC, SFA-5.14, typicalmechanical properties of conventional ERNiCr-3 weld metal include:tensile strength of 80 ksi. Also for comparison, MIL spec equivalentweld material (EN82H), MIL-E-21562, has a minimum tensile strength of 80ksi and a minimum elongation of 30%, and annealed UNS N06600 (ASTMB166/168), which has tensile strength and elongation values consistentwith EN82H, has a minimum yield strength (0.2% offset) of 35 ksi.Comparing properties of the as-tested inventive samples to theproperties of the comparative conventional sample, the as-testedinventive samples displayed an improvement in tensile strength of 14.0ksi to 22.0 ksi (corresponding to an improvement of 17.5% to 33.8%), in0.2% yield strength of 26.5 ksi to 38.5 ksi (corresponding to animprovement of 75.7% to 110%), and a change in elongation of −2% to +12%(corresponding to a decrease of 6.7% to an increase of 40.0%)

FIG. 3 contains a series of scanning electron micrographs taken at 20 kVand 1500× magnification showing the microstructure of samples of weldmaterial prepared using a shield gas (i) containing 0 mol. % nitrogen attwo locations (FIGS. 3A-B); (ii) containing 1 mol. % nitrogen at twolocations (FIGS. 3C-D); (iii) containing 5 mol. % nitrogen at twolocations (FIGS. 3E-F); and (iv) containing 20 mol. % nitrogen at twolocations (FIGS. 3G-H). FIGS. 3A-H show features similar to those shownand described with respect to FIG. 2, although with differing phasevolume of precipitates as the amount of nitrogen present during thewelding process was varied. As evident in the SEM micrographs, theincreased nitrogen content of the weld shielding gas and the resultantweld material (see Table 2) resulted in noticeable increases in MC- andMX-phase volume; both from increased distribution and size. Thecorresponding improvements to material strength can also be attributedto these precipitation increases, where such secondary phases are knownto impede the motion of dislocations through crystallographic structureof the material. Only subtle differences in mechanical properties andvolume fraction precipitates were noted between the 5 mol. % and 20 mol.% (in the mixed gas) nitrogen samples, however, likely due to thesolubility limit of the ERNiCr-3 weld material (i.e., bulk nitrogencontent of 1300-1400 ppm (in the weld metal).

In another example, welds formed of alloys of ERNiCr-3/EN82H wereinvestigated in which the nitrogen and carbon contents varied asfollows: 20-1400 ppm nitrogen and nominally 0.03 wt. % carbon ornominally 0.05 wt. % carbon. The welds materials were investigated fortensile properties in both the longitudinal direction and the transversedirection relative to the weld travel direction. Table 5 presents theresults of these investigations and, for each sample, reports tensilestrength (in ksi) and 0.2% yield strength (in ksi),

TABLE 5 Tensile Testing of Weld Materials Based on ERNiCr-3/EN82H Alloyswith Varying N and C Content Longitudinal Tensile Transverse TensileYield, Yield, C N Tensile 0.2% Elongation Reduction Tensile 0.2%Elongation Reeducation Sample (wt. %) (ppm) (ksi) (ksi) (% in 4D) inArea (%) (ksi) (ksi) (% in 4D) in area (%) YT0159 0.053 19 97 62.5 42 4694 63 36 43 0N YT0159 0.050 200 96.5 63.5 39 52 97 62 45 58 0.2N YT01590.050 310 97.5 62.5 37 53 97 61 40 46 0.4N YT0159 0.053 600 99 64.5 3751 97.5 61.5 38 42 1N YT0159 0.055 1300 104 69 35 38 107 73.5 28 38 5NYT0159 0.051 1400 102 67.5 31 39 107 72.5 35 40 20N B8142 0.030 130 89.557.5 37 60 93 59.5 40 49 0N B8142 0.030 275 95.5 58 44 59 100 65.5 39 540.2N B8142 0.028 345 95.5 57.5 37 52 94 57.5 41 54 0.4N B8142 0.027 57095 58 44 54 97.5 59.5 41 47 1N B8142 0.029 960 98.5 60.5 39 48 101 62.537 41 5N

In the above results in Table 5, the carbon content of the samples didnot vary the carbon outside of selecting two wire heats with a differentcarbon contents—a high carbon content of 0.05 wt. % and low carboncontent of 0.03 wt. %). Comparing data from samples with equivalent ornearly equivalent nitrogen content can be used to isolate carbon effectsin these samples. In this case and using the data from Table 5,comparing values for mechanical properties of sample YT0159 1N to sampleB8142 1N shows the effect of varying carbon content (0.05 wt. % C forYT0159 1N; 0.03 wt. % C for B8142 1N) with nominally constant nitrogencontent in the shield gas or 1 mol % N in mixed gas. For these samples,testing reported in Table 5 shows a reduction in longitudinal mechanicalproperties between the samples, but the transverse mechanical propertiesare nominally constant. In another case and using the data from Table 5,comparing values for mechanical properties of sample YT0159 0.4N tosample B8142 0.4N shows the effect of varying carbon content (0.05 wt. %C for YT0159 0.4N; 0.03 wt. % C for B8142 0.4N) with nominally constantnitrogen content in the shield gas or 0.4 mol % N in mixed gas. Forthese samples, testing reported in Table 5 shows a nominal constantvalue in longitudinal mechanical properties between the samples, but thetransverse mechanical properties are show a reduction in values for thelow carbon sample (0.03 wt. % C) as compared to the high carbon sample(0.05 wt. % C).

One conclusion from the above investigation is that nitrogen has aminimal effect on tensile and yield strength and that carbon has astronger effect than nitrogen on tensile and yield strength.Additionally, the difference in solubility of nitrogen in the low carbonsample B8142 5N as compared to the sample YT0159 5N for the same amountof nitrogen in the shield gas is noteworthy and suggests/confirms thatstarting material content, most notably of carbon (and to a lesserextent Ti and Nb), will have a direct influence on nitrogen solubilityduring and after the welding/melting process(es). These effects are alsoanticipated via non-equilibrium computational thermodynamic modeling andare expected to be observable during primary/secondary melting processesof bulk material production or product manufacturing. This providesinsight to the interdependence of carbon and nitrogen content and theconsideration required to achieve target material composition; both inoriginal product form or throughout manufacturing.

Also, one can compare the mechanical properties of various samples toobserve the effect of varying nitrogen content in the shield gas forboth nominal 0.05 wt. % C and nominal 0.03 wt. % C samples using ashield gas with 5 mol. % nitrogen (the 5N samples) to the correspondingsamples prepared using a shield gas with 0 mol. % nitrogen, one canobserve the change in mechanical properties as the amount of nitrogen inthe shield gas (and, by proxy the amount of nitrogen in the weldmaterial, increase. The changes in tensile strength (absolute and inpercentage) are shown in Table 6.

TABLE 6 Comparison of mechanical properties of samples prepared with 5mol. % nitrogen shield gas to mechanical properties of a sample preparedwith 0 mol. % nitrogen shield gas Change in Change in Yield Direction ofTensile Strength Strength, 0.2% Sample measurement (ksi/%) (ksi/%)YT0159-5NC longitudinal 7.0 ksi/7.2%  6.5 ksi/10.4% transverse 13.0ksi/13.8% 10.5 ksi/16.7% B8142-5NC longitudinal  9.0 ksi/10.1% 3.0ksi/5.2% transverse 8.0 ksi/8.6% 3.0 ksi/5.0%

One conclusion from the above investigation is that an increase innominal material carbon content will increase the anticipated range ofmaterial strength within the respective boundaries of nitrogensolubility (as influenced by the weld/melt process) or, alternately, adecrease in nominal material carbon content will restrict theanticipated influence of material strength due to varied nitrogencontent.

Although the present invention has been described in connection withembodiments thereof, it will be appreciated by those skilled in the artthat additions, deletions, modifications, and substitutions notspecifically described may be made without departure from the spirit andscope of the invention as defined in the appended claims. For example,although described in relation to weld material, the principles,compositions and processes described herein can also apply to basematerials and their compositions and can be implemented in the alloyingprocessing of base materials.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations are not expressly set forth herein for sakeof clarity.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures may beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled,” to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable,” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents, and/or wirelessly interactable, and/or wirelesslyinteracting components, and/or logically interacting, and/or logicallyinteractable components.

In some instances, one or more components may be referred to herein as“configured to,” “configured by,” “configurable to,” “operable/operativeto,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc.Those skilled in the art will recognize that such terms (e.g.,“configured to”) can generally encompass active-state components and/orinactive-state components and/or standby-state components, unlesscontext requires otherwise.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true spirit and scope of the subject matter described herein.It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to claims containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that typically a disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms unless context dictates otherwise. For example, the phrase “Aor B” will be typically understood to include the possibilities of “A”or “B” or “A and B.”

With respect to the appended claims, those skilled in the art willappreciate that recited operations therein may generally be performed inany order. Also, although various operational flows are presented in asequence(s), it should be understood that the various operations may beperformed in other orders than those which are illustrated, or may beperformed concurrently. Examples of such alternate orderings may includeoverlapping, interleaved, interrupted, reordered, incremental,preparatory, supplemental, simultaneous, reverse, or other variantorderings, unless context dictates otherwise. Furthermore, terms like“responsive to,” “related to,” or other past-tense adjectives aregenerally not intended to exclude such variants, unless context dictatesotherwise.

Those skilled in the art will appreciate that the foregoing specificexemplary processes and/or devices and/or technologies arerepresentative of more general processes and/or devices and/ortechnologies taught elsewhere herein, such as in the claims filedherewith and/or elsewhere in the present application.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

The illustrative embodiments described in the detailed description,drawings, and claims are not meant to be limiting. Other embodiments maybe utilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented here.

One skilled in the art will recognize that the herein describedcomponents (e.g., operations), devices, objects, and the discussionaccompanying them are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated.Consequently, as used herein, the specific exemplars set forth and theaccompanying discussion are intended to be representative of their moregeneral classes. In general, use of any specific exemplar is intended tobe representative of its class, and the non-inclusion of specificcomponents (e.g., operations), devices, and objects should not be takenas limiting.

What is claimed is:
 1. A method of fusion welding, comprising: forming aregion of molten material in contact with at least one metallic body,wherein the molten material includes molten base metal from the metallicbody, weld metal from a welding alloy, and, optionally, one or moremolten additive material; modifying at least one of a nitrogen contentof the molten material, a nitride content of the molten material, acarbon content of the molten material, and a carbide content of themolten material; coalescing the molten material; and solidifying themolten material to form a weld material, wherein the weld material joinsto the metallic body to form a weldment, wherein the solidified weldmaterial in the weldment has a composition including: Cr 18.0 to 22.0wt. %, Mn 2.5 to 3.5 wt. %, Fe up to 3.0 wt. %, N 15 ppm to 200 ppm, andC up to 0.040 wt. %

wherein a microstructure of the solidified weld material in the weldmentincludes a plurality of precipitates, wherein the plurality ofprecipitates include a plurality of metal carbide precipitates and aplurality of metal carbide/nitride precipitates, and wherein a volumefraction of the plurality of precipitates is 0.0025 or less for nitrogenin the range of 15 ppm to 200 ppm.
 2. The method of claim 1, wherein thecomposition of the weld material in the weldment further comprises: Nb +Ta 2.0 to 3.0 wt. % Ti up to 0.75 wt. %, Si up to 0.25 wt. %, and Niequal to or greater than 67 wt. %.


3. The method of claim 1, wherein the volume fraction of the pluralityof precipitates is 0.0025 for nitrogen of 100 ppm in combination with0.03 wt. % C.
 4. The method of claim 1, wherein a microstructure of theweld material in the weldment includes a plurality of NbC precipitates.5. The method of claim 1, wherein modifying the nitrogen contentincludes adding nitrogen to the region of molten material.
 6. The methodof claim 1, wherein the weldment includes the at least one metallic bodyand a second metallic body joined by the weld material.
 7. The method ofclaim 6, wherein the at least one metallic body and the second metallicbody are dissimilar metals.
 8. The method of claim 1, wherein a contentof nitrogen in the composition of the solidified weld material in theweldment is 15 ppm to 100 ppm, and wherein the volume fraction of theplurality of precipitates is 0.0018 or less.
 9. The method of claim 1,wherein the volume fraction of the plurality of precipitates is 0.0025for nitrogen of 125 ppm in combination with 0.03 wt. % C.
 10. The methodof claim 1, wherein a content of Cr in the composition of the solidifiedweld material in the weldment is 18.0 to 20 wt. %.